1. Field of the Invention
The present invention relates to a method and a system for suppressing a surface oxide film during hot finish rolling of a strip material.
2. Description of Related Art
When iron contacts a gas, such as oxygen or air, at a high temperature during rolling of a strip material, a film of the reaction product, i.e., scale, is formed on the surfaces of the strip material. This scale may exert an adverse influence, such as oxidation, on the strip material, and should be removed. The customary practice for removing scale formed on a strip material has been to apply a jet of pressurized water at the surface of the strip material.
FIG. 8 is a schematic view illustrative of a scale removing device of a conventional hot finishing mill system.
With a conventional hot finishing mill system as shown in FIG. 8, a plurality of finishing mills, i.e., 1st to 7th finishing mills 101, 102, 103, 104, 105, 106, and 107, are provided in a row along the direction of transport of a rolled material S downstream of a roughing mill (not shown) in the direction of transport. The finishing mills 101, 102, 103, 104, 105, 106, and 107 have a pair of (i.e., upper and lower) work rollers 201, 202, 203, 204, 205, 206, and 207, respectively. A finishing mill group 100 is constructed in this manner. On the entry side of this finishing mill group 100, a scale breaker 301 is provided for removing scale formed on the rolled material S. The scale breaker 301 has jet nozzles 302 above and below the rolled material S. These jet nozzles 302 direct jets of water at a high pressure of, for example, 200 kgf/cm.sup.2, at upper and lower surfaces of the rolled material S to remove the scale.
Thus, the rolled material S transported after rough rolling from a slab by a roughing mill is conveyed to the entry side of the finishing mill group 100, where scale formed on the surfaces of the rolled material S is removed by the scale breaker 301 before finish rolling. In detail, water pressurized at, for example, 200 kgf/cm.sup.2, is jetted through the upper and lower jet nozzles 302 at the upper and lower surfaces of the conveyed rolled material S to remove the adhering scale. The descaled rolled material S is then carried to the finishing mill group 100 for rolling by the work rollers 201, 202, 203, 204, 205, 206, and 207 of the 1st to 7th finishing mills 101, 102, 103, 104, 105, 106, and 107, where it is sequentially finish rolled to predetermined thicknesses.
With such a hot finishing mill system, when the duration of contact of the rolled material S with the work rollers 201, 202, 203, 204, 205, 206, and 207 is relatively long, the quality of the processed product improves; however, the formation of scale is accelerated. Thus, a conventional method for suppressing the formation of scale has been to cool the rolled material S before finish rolling. This method suppresses scale formation to some degree; however, further suppression of scale and further improvement in quality are desired for hot rolled products.